Currently, there are a variety of magnetic stirrers used for suspending biological cells, or tissue growths, in a liquid growing medium. These stirrers typically include a vessel and a closure having a stirring member, or paddle assembly, consisting of a magnet that spins about a vertical axis upon subjecting the stirring assembly to a rotating magnetic field. The stirring assembly may also include paddles that are designed to stir the cell culture at relative slow speeds to avoid damaging the cells as they are being mixed into the growing medium.
U.S. Pat. No. 4,512,666 discloses a prior art adjustable-height magnetic stirrer having a suspended magnetic impeller that is vertically adjustable by rotating a threaded sleeve member disposed within a threaded support member. By rotating the threaded sleeve member, the magnetic impeller rises up or down, depending on the direction of rotation, due to it being attached to a bearing surface at the end of the threaded sleeve member.
U.S. Pat. No. 4,512,666 also discloses a vessel having access ports extending outwardly from the side walls of the vessel at an angle to allow pipettes or other instruments to be inserted into the vessel to gain access to cultures therein. U.S. Pat. No. 4,512,666 further discloses a closure having a gas permeable membrane allowing for the exchange of gases to the ambient while minimizing the risk of contaminating the cell culture within the vessel.
Shortcomings with prior art apparatus, including the apparatus disclosed in U.S. Pat. No. 4,512,666, is that specially designed vessels having access ports must be obtained and used if quick and convenient access to the cell culture contained therein is to be achieved. Additionally, such access ports may provide only a limited amount of access to certain areas of the interior of the vessel due to the stirring member, or paddle assembly, blocking the port. Therefore, it may be necessary to remove the closure to reach those areas thereby increasing the chances of contaminating the culture contained therein.
A further shortcoming with stirring vessels having access ports protruding from the sides thereof, is the ports often interfere with each other when packing the vessels closely together for storage. The ports also interfere with each other when placed close to each other on magnetic stirring plates large enough to accommodate several vessels simultaneously.
Furthermore, such vessels having access ports are relatively expensive due to their inherent construction costs. Expenses can be compounded if the vessels must be replaced due to being broken during usage or storage.